The present invention relates to a process for manufacturing a molded circuit board for an internal antenna or the like by plating portions of the surface of a molded member or the inner surface of an aperture provided in the molded member.
The present inventors previously suggested a process for manufacturing a partially-plated plastic molded product. For manufacturing a circuit substrate, for example, the method comprises the steps of: molding a circuit substrate as a primary molded member in dies; roughening the surface of the substrate, applying catalyst to the substrate for pre-treatment, placing the pre-treated substrate in dies; coating the substrate with plastic material except for a portion of the substrate on which a circuit is to be formed such that the circuit substrate is covered with the plastic but with only the circuit portion remaining uncovered, by which a circuit substrate as a secondary molded member is produced; and plating the substrate to produce a final product of the circuit substrate with only the circuit portion plated.
In such processes, however, the material that is molded in the second molding step (i.e., secondary molded member) will remain in the final product. Accordingly, if a mixture of fillers such as glass fiber is used as a plastic material for the second molding step, the production cost will rise. Alternatively, if resin is used as a second molding material, as the resin needs high-pressure injection, the circuit portion of the substrate is required to be thicker and wider, causing the whole body of the substrate to be larger, and therefore there is a limit to making the circuit substrate, as the final product, thin and compact.
Accordingly, an object of the present invention is to provide a method for manufacturing a molded circuit board with its size as small as possible by eluting the secondary molded member in an intermediate step of its manufacturing process. Another object is to avoid the environmental pollution in the elution step by using biodegradable resin as the material for the secondary molded member. A further object is to reduce production cost by using material that can be eluted easily and simplifying the procedure.
For the above-described objects, the process for manufacturing a molded circuit board according to the present invention comprises the following steps. A first step is molding a primary molded member by injecting liquid crystal polymer of plating grade in a cavity that has an outline corresponding to the dimensions of the molded circuit board. A second step is roughening the surface of the primary molded member. A third step is molding a secondary molded member by inserting the primary molded member into a cavity formed in such a shape that when said primary molded member is inserted thereinto, a gap is provided around the surface of the primary molded member except for a portion thereof on which a circuit is to be formed and then injecting the oxylkylene-containing poly(vinyl alcohol) resin into the cavity. A fourth step is heating the first and secondary molded members as a whole in a stream of hot air to improve the water resistance thereof. A fifth step is applying a catalyst such as palladium and/or gold on the portion of the surface of the primary molded member on which the circuit is to be formed. A sixth step is heating the first and secondary molded members as a whole in hot water to elute the secondary molded member into the hot water. And a seventh step is plating the catalyst-applied portion of the primary molded member to form the circuit.
Liquid crystal polymer of plating grade may be used as a material for the primary molded member due to the following favorable properties. First, as liquid crystal polymer of plating grade has solder-heat-resistance, it can provide greater resistance against solder reflow when a circuit is formed on the surface of the primary molded member. Second, as the polymer exhibits a unique structure called a xe2x80x9cskin layerxe2x80x9d on its surface, it can provide greater releasability of the primary molded member from the secondary molded member.
Further, oxyalkylene-containing poly(vinyl alcohol) may preferably be used for the material of the secondary molded member due to the following properties. First, as oxyalkylene-containing poly can be easily melted and molded, it is suitable for injection molding. Second, as it is water-soluble, it can be eluted easily. Third, as it is biodegradable, it can be reduced to naturally existing materials without polluting the surrounding environment.